Eating a cricket may not have been too bad, it was the wriggling maggots Prime Minister John Key found hard to stomach.

Key was "briefly" and "incognito" in the audience at television survival star Bear Grylls live show in Auckland last night, along with son Max and wife Bronagh.

"He (Grylls) got me up on stage, and I had to eat a cricket, but the worst came when he gave me a huhu grub with ... live maggots that were wriggling down the back of my throat," Key told TVNZ's Breakfast programme.

On NewstalkZB he said: "Let me give you a clue, don't eat the maggots."

"The cricket was fine," Key told Radio Live. "Eating, crunching through the live cricket was all right, but the huhu grub, he puts a pinch of maggots in there, little maggots. You couldn't bite them fast enough to kill them so they're wriggling down the back of your throat, then they're wriggling back up, and I had to pull them out from in between my teeth."

But Key was hopeful the willingness to test his constitution in public could help him with the voters, after a One News-Colmar Brunton poll showed Labour's party vote lift 3 percentage points to 35 per cent, with the Greens up one on 13 per cent, while National was down one on 44 per cent.

"I reckon I might regain one of those points tomorrow from Bear Grylls lovers," Key said on Breakfast.